OPERATING INSTRUCTIONS
MODEL PRH-09THD
PRESSURE REDUCING VALVE
Phone: 973-340-9955 Fax: 973-340-9933
http://www.straval.com Email: [email protected]
OPERATING INSTRUCTIONS
The packing rings expand under pressure and therefore should
not be over tightened. If the packing rings are over tightened,
the valve will not be very responsive to pressure changes or not
even regulate at all. It is usually sufficient to make the packing
nut hand tight and add 1/4 to 1/2 turn with a wrench. Finally
when the valve is installed in the line without the spring cham-
ber any additional tightening may be performed while under
pressure, if there still any leakage through the v-packing rings.
After this adjustment is performed, the spring chamber and
spring hardware may be installed. Next inspect the seat and
main valve in the area where sealing contact is made. It may
be necessary to just re-lap these parts with a fine grit lapping
compound such as A#600 grit. If there is more severe wear or
damage that can’t be corrected by lapping, then the parts need
to be replaced or re-machined making sure that the parts re-
main concentric. Also, inspect the main valve in the area where
the teflon-v-packing rings perform their sealing function.
If the area is not too severely worn, the surface may be re-
polished and restored to a smooth low friction surface finish. If
this area is very rough or worn, the valve will not regulate
properly and will stick because of excessive friction and wear. If
in doubt, replace the entire main valve from the factory. It is
generally recommended that the valve be overhauled by replac-
ing the main valve, and v-packing rings, in order to restore the
valve in an as new condition. If the main valve is purchased
from the factory, it must be lapped into the body at final assem-
bly for optimum regulating performance, particularly if the valve
is operating in a low flow mode where the valve travel is very
small and the clearance through the valve seat is very small.
After the valve is properly assembled, reset the adjusting screw
until the desired outlet pressure is achieved at the flow range
the valve will be operating, then tighten the adjusting screw lock
nut. Little or no adjustment is required to compensate for
changes in inlet pressure, as this valve is a balanced design.
Adjust the spring compression by loosening the lock nut and
turn the adjusting screw clockwise to increase the spring com-
pression; this will increase the outlet pressure. Similarly, turning
the screw counterclockwise will reduce the spring compression
and correspondingly reduce the outlet pressure. A slow pressure
build up will take place if the outlet is completely blocked off
which may take place over a period of time depending on how
effective the valve seat is performing and the volume of the dis-
charge piping. For this reason
it is strongly recommended
that a relief valve be installed on the outlet side of the
valve to protect any equipment damage
that may take place
because of this possible pressure build up in a shut off or
blocked discharge condition. If the regulator fails to maintain the
proper outlet pressure, there could be a number of probable
causes as follows: Packing nut may be over tightened, Internal
clogging of foreign objects or material, sediment, rust, etc. in
the valve seat area. If disassembly is required make sure the
valve piping is not under pressure and sufficiently cooled off for
operating personnel to handle. When a valve is ordered with
socket weld connections, the valve seat must be re-lapped by
the customer after the valve is welded to the piping. Every pre-
caution should be made to minimize distortion due to excessive
heat during welding. Depending on the degree of distortion
caused by welding, it is recommended that lapping be performed
with several course grit grades first, and finally finishing with a
#600 or better yet a #800 grit to get the best seat finish.
